1. Field of the Invention
Illustrative embodiments of the present invention relate to an ink cartridge and an image forming apparatus, and more specifically, to an image forming apparatus having a recording head that ejects droplets and an ink cartridge detachably mounted in the image forming apparatus.
2. Description of the Background
Image forming apparatuses are used as printers, facsimile machines, copiers, plotters, or multi-functional peripherals having two or more of the foregoing capabilities. As one type of image forming apparatus employing a liquid-ejection recording method, an inkjet recording apparatus is known that ejects liquid droplets from a recording head onto a recording medium to form a desired image.
Such an inkjet-type image forming apparatus falls into two main types: a serial-type image forming apparatus that forms an image by ejecting droplets while moving a recording head in a main scan direction, and a line-head-type image forming apparatus that forms an image by ejecting droplets from a linear-shaped recording head fixedly disposed in the image forming apparatus.
Such an inkjet-recording-type image forming apparatus (hereinafter, an “inkjet recording apparatus”) may have a sub tank (buffer tank or head tank) mounted on a carriage on which the recording head is mounted and a main ink cartridge (main tank) detachably mounted in the image forming apparatus. In such a case, ink is supplied (filled) from the ink cartridge to the sub tank.
For example, conventional ink cartridges like those described in Japanese Patent Application Laid-Open Nos. 2004-306505 and 2003-220710 have a cartridge case that houses a double pack including an inner pack and an outer pack. The inner pack serves as an ink pack to store ink. The outer pack packs the inner pack and has a space outside the inner pack into which compressed air is introduced. By the compressed air introduced into the outer pack, the inner pack is pressed to supply ink to the recording head.
However, in the above-described conventional ink cartridges having the double pack structure, since the size of the outer pack into which air is introduced is smaller than the capacity of the cartridge case, the outer pack endures by itself air pressure applied to supply a good amount of ink. Such a configuration may require an enhanced strength of the outer pack. Further, if the outer pack is formed by welding, the strength of welding need be enhanced.
In particular, the capacity of ink cartridge has recently been increased to meet a demand for raising the image formation speed while stably supplying ink. However, since an increased pressure in the outer pack might burst the outer pack, the above-described conventional ink cartridge may not achieve ink supply compatible with stable high-speed printing. Further, since the internal pressure of the outer pack is proportional to the area of the outer pack, the outer pack might break from a welded portion due to internal pressure when the outer pack is formed by welding in a large capacity of ink cartridge. Accordingly, such a large capacity may not be easily achieved in the above-described conventional ink cartridge. Alternatively, it is conceivable that by increasing the thickness of the outer pack, the strength of the outer pack may be enhanced so as to endure a high pressure. However, such a configuration may prevent cost reduction.